Production of titania

ABSTRACT

A process for producing titania from a solid, iron-containing titaniferous material (such as ilmenite) is disclosed. The process includes a first step of treating iron-containing titaniferous material under conditions that reduce ferric ions to ferrous ions in the titaniferous material. Thereafter the process include steps of leaching treated titaniferous material and forming a leach liquor that includes an acidic solution of titanyl sulfate and iron sulfate and recovering titania from the leach liquor.

The present application is a continuation-in part application of andclaims priority to PCT/AU2005/000387 published in English on Sep. 29,2005 as PCT WO 2005/090619 and from AU 2004901444 filed Mar. 18, 2004,the entire contents of each are incorporated herein by reference intheir entirety.

BACKGROUND

The present invention relates to a process for producing titania from atitaniferous material.

The term “titaniferous” material is understood herein to mean anytitanium-containing material, including by way of example, ores, oreconcentrates, and titaniferous slags.

The present invention relates particularly to a process for producingtitania from a solid titaniferous material that can be described ingeneral terms as a sulfate process.

The term “sulfate” process is understood herein to mean a process forproducing titania from a titaniferous material that comprises treating asolid feed material and at least substantially dissolving the feedmaterial into solution and thereafter recovering titania from solution.

The applicant has been carrying out research and development work inrelation to the sulfate process. The work has resulted in two optionsfor the sulfate process.

One process option is described in US 2006/0177363 (Internationalapplication PCT/AU03/01386 published as WO 2004/035843) and the otherprocess option is described in US 2005/180903 (International applicationPCT/AU2004/001421 published as WO 2005/038060).

Both process options include the steps of:

-   -   (a) leaching solid, iron-containing titaniferous material, such        as ilmenite, with a leach solution containing sulfuric acid and        forming a leach liquor that includes an acidic solution of        titanyl sulfate (TiOSO₄) and iron sulfate (FeSO₄);    -   (b) separating titanyl sulfate from the leach liquor, for        example by solvent extraction as described in International        application PCT/AU03/01386 or precipitation as described in        International application PCT/AU2004/001421; and    -   (c) recovering titania from the titanyl sulfate.

The research and development work included leaching ilmenite in 400-750g/l sulfuric acid. The work included adding iron in the form of scrapiron during the leaching step (a). The main advantage of adding iron isto accelerate the rate of leaching. The disadvantages of adding ironinclude increased amounts of iron sulfate as a by-product and increasedprocess complexity (such that an industrial plant would need equipmentfor handling scrap iron and for dealing with hydrogen gas that isevolved as a consequence of iron addition). In addition, scrap iron,although not expensive currently, introduces an additional operatingcost to the process. In addition, the leaching rate is such, even withthe addition of iron, that it may still be necessary to grind ilmeniteprior to the leaching step to improve the rate.

The applicant has found in further research and development work that itis possible to achieve leaching rates that are comparable to leachingrates achieved with the addition of scrap iron in the leaching step (a)by treating ilmenite prior to the leaching step under conditions thatreduce ferric ions to ferrous ions in the ilmenite. The conditionsinclude contacting the titaniferous material with a reducing gas. Theilmenite treatment step makes it possible to avoid or at least minimizescrap iron addition during the leaching step.

BRIEF SUMMARY

The present invention provides a method for producing titania from asolid, iron-containing titaniferous material (such as ilmenite) thatincludes the steps of: treating iron-containing titaniferous materialunder conditions that reduce ferric ions to ferrous ions in thetitaniferous material, the conditions including contacting thetitaniferous material with a reducing gas; leaching treated titaniferousmaterial and forming a leach liquor that includes an acidic solution oftitanyl sulfate and iron sulfate; and recovering titania from the leachliquor.

Additional features and benefits of the present invention are describedand will be apparent from the accompanying drawings and detaileddescription below.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate embodiments of the inventionaccording to the practical application of the principles described andshown.

FIG. 1 shows the results of the treatment of Stradbroke ilmenite with areducing gas in a thermogravimetric analysis apparatus.

FIG. 2 shows the results of the treatment of Stradbroke ilmenite in aHot Reduction Rig.

FIG. 3 is a plot of titanium extraction versus leach time where theilmenite was reduced under different temperature conditions.

FIG. 4 is a plot of titanium extraction versus leach time where theilmenite was reduced under different partial pressures of CO at the sametemperature.

DESCRIPTION

The applicant has found in further research and development work that itis possible to achieve leaching rates that are comparable to leachingrates achieved with the addition of scrap iron in the leaching step (a)by treating ilmenite prior to the leaching step under conditions thatreduce ferric ions to ferrous ions in the ilmenite. The conditionsinclude contacting the titaniferous material with a reducing gas. Theilmenite treatment step makes it possible to avoid or at least minimizescrap iron addition during the leaching step.

Accordingly, the present invention provides a process for producingtitania from a solid, iron-containing titaniferous material (such asilmenite) which includes the steps of:

-   -   (a) treating iron-containing titaniferous material under        conditions that reduce ferric ions to ferrous ions in the        titaniferous material, the conditions including contacting the        titaniferous material with a reducing gas;    -   (b) leaching treated titaniferous material and forming a leach        liquor that includes an acidic solution of titanyl sulfate and        iron sulfate;    -   (c) recovering titania from the leach liquor.

Preferably, step (a) comprises treating titaniferous material underconditions that result in ferrous ions being a predominant form of ironin the titaniferous material.

The term “predominant” is understood to herein to mean that the amountof ferrous ions is a major part of the total amount of iron in thetreated material. In terms of the actual amount of ferrous ions in thetreated material, this may mean that the amount of ferrous ions is atleast 40%, typically at least 50%, by weight of the total weight of ironin the treated material. In terms of the increase in ferrous ions fromthe amount of ferrous ions in the titaniferous material prior totreatment step (a), this may mean that there is an increase in ferrousions by at least 50% of the amount of ferrous ions in the titaniferousmaterial prior to treatment step (a).

Preferably, step (a) comprises treating titaniferous material underconditions that do not result in substantial formation of rutile that isunleachable under the conditions of leaching step (b).

Preferably, step (a) comprises treating titaniferous material underconditions so that there is either no metallic iron formed in the stepor a selected relatively small amount of metallic iron formed in thestep.

Step (a) may be carried out in any suitable treatment apparatus such asa fluidized bed or a kiln.

Preferably, step (a) comprises treating titaniferous material bycontacting titaniferous material with the reducing gas in a fluidizedbed.

The relevant conditions for step (a) include by way of example theselection of (i) the composition of the reducing gas, (ii) thetemperature of the reducing gas, and (iii) the contact time of thereducing gas and the titaniferous material.

The reducing gas may be any suitable gas, such as hydrogen, carbonmonoxide, and mixtures thereof.

Preferably, the reducing gas is a mixture of (a) hydrogen and/or carbonmonoxide and/or methane and (b) another suitable gas such as an inertgas and/or carbon dioxide.

Preferably, the inert gas is nitrogen.

In a situation in which the reducing gas comprises hydrogen and theinert gas comprises nitrogen, preferably the hydrogen comprises up to25%, more preferably 3-25%, by volume of the reducing gas.

In a situation in which the reducing gas comprises hydrogen, preferablythe temperature of the reducing gas is less than 700° C. to avoidsubstantial formation of rutile that is unleachable under the conditionsof leaching step (b).

In a situation in which the reducing gas comprises hydrogen, preferablythe temperature of the reducing gas is 450-550° C.

In a situation in which the reducing gas comprises carbon monoxide andthe other gas comprises carbon dioxide, preferably the carbon monoxidecomprises up to 60%, more preferably 30-60%, by volume of the reducinggas.

In a situation in which the reducing gas comprises carbon monoxide andthe inert gas comprises nitrogen, preferably the temperature of thereducing gas is less than 700° C., more preferably less than 650° C.

In a situation in which the reducing gas comprises carbon monoxide andthe inert gas comprises nitrogen, it is preferred particularly that thetemperature of the gas be 600° C.

Preferably, the average contact time of the material and the reducinggas is less than 120 minutes, more preferably 20-120 minutes.

Steps (b) and (c) may be as described in US 2006/0177363 (Internationalapplication PCT/AU03/01386 published as WO 2004/035843) and the otherprocess option is described in US 2005/180903 (International applicationPCT/AU2004/001421 published as WO 2005/038060), the entire contents ofeach are incorporated herein by reference.

Specifically, the leaching step (b) may comprise a multiple leachingstep involving (i) a first step of leaching the titaniferous materialwith the leach liquor and forming a process solution that includes anacidic solution of titanyl sulfate; (ii) separating the process solutionand a residual solid phase; (iii) leaching the residual solid phase in asubsequent leach step with a leach liquor and forming a further processsolution that includes an acidic solution of titanyl sulfate and ironsulfate; (iv) separating the process solution and a residual solidphase; and (v) supplying the separated process solution to the firstleach step and/or mixing the separated process solution with the processsolution from the first leach step for subsequent processing in reducingstep (c).

Preferably, the leaching step (b) includes selecting and/or controllingthe leaching conditions to avoid undesirable amounts of prematurehydrolysis and undesirable amounts of premature precipitation.

Typically, the acid concentration in the leaching step (b) should be atleast 350 g/l sulfuric acid throughout the leaching step when operatingat a leach temperature in the range of from 95° C. to the boiling pointin order to avoid premature hydrolysis.

Furthermore, typically, the acid concentration at the end of theleaching step (b) should be less than 450 g/l when operating at a leachtemperature in the range from 95° C. to the boiling point in order toavoid an undesirable amount of premature precipitation of titanylsulfate.

The acid concentration at the start of the leaching step (b) may behigher than the above desirable concentrations, typically as high as 700g/l.

Specifically, step (c) of recovering titania from the leach liquor maycomprise the steps of (i) separating iron sulfate from the leach liquor,(ii) separating titanyl sulfate from the leach liquor either after orbefore step (i), and (iii) recovering titania from the titanyl sulfate.

More specifically, step (ii) of separating titanyl sulfate from theleach liquor may comprise solvent extraction of titanyl sulfate from theleach liquor, as described in US 2006/0177363 (International applicationPCT/AU03/01386 published as WO 2004/035843).

A further, although not the only other possible option for step (ii) ofseparating titanyl sulfate from the leach liquor comprises precipitatingtitanyl sulfate from the leach liquor, as described in US 2005/180903(International application PCT/AU2004/001421 published as WO2005/038060).

Steps (b) and (c) are not confined to the steps described in US2006/0177363 (International application PCT/AU03/01386 published as WO2004/035843) and the other process option is described in US 2005/180903(International application PCT/AU2004/001421 published as WO2005/038060).

For example, the leaching step (b) may be in accordance with thestandard sulfate process, which includes a 2-stage step with a firststage involving solid state sulfation of pre-treated titaniferousmaterial from step (a) with concentrated sulfuric acid and a secondstage involving dissolving the sulfated product in water/dilute acid andforming an acidic solution of titanyl sulfate and iron sulfate.

The research and development work carried out by the applicant inrelation to treatment of ilmenite has focused on the use of hydrogen gasand carbon monoxide.

The following description relates to the research and development workcarried out at the Newcastle Technology Centre of the applicant.

Overview of Feed Materials and Experimental Parameters.

Based on promising results in the experiments on Beenup ilmenite, asecond set of treatment experiments was carried out using ilmenite fromtwo batches of Stradbroke ilmenite. The following description discussesthese experiments.

A further set of experiments including reducing gases containing carbonmonoxide was carried out on Cruzor (trade mark) ilmenite. The followingdescription discusses these experiments.

Stradbroke Ilmenite Experiments.

The experiments on the first batch of Stradbroke ilmenite concentratedon the impact of three variables on treatment of ilmenite. The variableswere:

-   -   (a) reducing gas temperature—450° C. and 550° C.;    -   (b) gas composition—10% H₂ in N₂ and 20% H₂ in N₂; and    -   (c) reduction time—45 minutes and 90 minutes.

The experiments on the second batch of Stradbroke ilmenite concentratedon confirming the results of treatment on the first batch of Stradbrokeilmenite and generating comparative data to provide a basis to assessthe treatment.

Particle size of Feed Materials.

Table 1 sets out the particle size distribution of the first batch ofStradbroke ilmenite. TABLE 1 Sizing data for 1^(st) Batch of StradbrokeIlmenite. Size (mm) Weight (g) % % passing 1 0 0.000 100.000 0.5 0 0.000100.000 0.425 0.1 0.023 99.977 0.3 0.8 0.187 99.790 0.25 3.7 0.86598.925 0.18 43.4 10.143 88.782 0.125 172.8 40.383 48.399 0.109 85.920.075 28.324 0.09 88.4 20.659 7.665 0.063 32.4 7.572 0.093 0.053 0.20.047 0.047 0.038 0.1 0.023 0.023 Total: 219.2 100

Table 2 sets out the particle size distribution of the second batch ofStradbroke ilmenite. TABLE 2 Sizing data for 2^(ND) Batch of StradbrokeIlmenite. Size (mm) Weight (g) % % passing 1 0 0.000 100.000 0.5 0 0.000100.000 0.425 0 0.000 100.00 0.355 0.2 0.044 99.956 0.3 0.7 0.156 99.8000.25 4.5 1.001 98.799 0.18 43.9 9.763 89.073 0.125 166.6 37.047 51.9900.106 79.9 17.678 34.312 0.09 105.3 23.416 10.896 0.063 47.3 10.5180.378 0.053 1.2 0.267 0.111 0.038 0.4 0.089 0.022 −0.038 0.1 0.022 0.000Total: 449.7 100

The first and second batches of the Stradbroke ilmenite had similarparticle size distributions and were finer in particle size than theBeenup ilmenite. Specifically, whilst the top size was smaller, thebottom size was the same as that of Beenup ilmenite.

Thermogravimetric Analysis Apparatus Tests.

The impact of treatment of the first batch of Stradbroke ilmenite with areducing gas in accordance with the invention was evaluated first in athermogravimetric analysis apparatus (“TGA”).

The full size fraction of the first batch of the Stradbroke ilmenite asset out in Table 1 above was selected for use in the TGA experiments, asthe finest fraction was large enough to resist terminal velocity at 12l/min gas flow.

In addition, the use of the “as received” size fraction also had abenefit of minimizing further beneficiation through sizing or crushingat either a mine site or plant scale production.

Eight experiments were completed on 10 g samples of the first batch ofthe Stradbroke ilmenite. The experiments evaluated the impact of thethree variables of gas composition, temperature, and time, as describedabove.

The experiments monitored the weight loss of the samples during thecourse of the experiments.

A matrix of the variables is given in Table 3. TABLE 3 Matrix ofvariables for TGA tests. Temperature Time Gas Composition Low 450° C. 4510% H₂ in N₂ High 550° C. 90 20% H₂ in N₂

A summary of experimental conditions and the weight loss during thetreatment in the TGA tests is shown in Table 4. TABLE 4 Result summaryfor TGA Tests. Test Temp Gas Time Weight Loss % STR-IR0-L1 n/a n/a n/an/a STR-IR1-L1 450 10% H₂ in N₂ 45 1.35 STR-IR2-L1 450 10% H₂ in N₂ 901.46 STR-IR3-L1 550 10% H₂ in N₂ 45 1.63 STR-IR4-L1 550 10% H₂ in N₂ 901.74 STR-IR5-L1 450 20% H₂ in N₂ 45 1.37 STR-IR6-L1 450 20% H₂ in N₂ 901.45 STR-IR7-L1 550 20% H₂ in N₂ 45 1.68 STR-IR8-L1 550 20% H₂ in N₂ 902.04

The results of the TGA experiments indicate that the treatment steppartially reduced the ilmenite and did not completely reduce theilmenite, i.e. to the point of formation of 100% metallic iron.

An example of the results in this regard is shown in FIG. 1. The figureshows that there was substantial weight loss in the first 20 minutes ofthe experiment and that thereafter the weight loss was at a constant,relatively shallow, gradient to the time that the experiment wasstopped. The constant gradient weight loss is consistent with what wouldbe expected with reduction of ferric ions to ferrous ions. If reductionhad been completed, i.e. with formation of 100% metallic iron, it wouldhave been expected that the weight loss plot would have plateaued at alower level.

The trend shown in FIG. 1 was repeated in the other tests.

Leaching Tests on TGA Treated Ilmenite.

The treated ilmenite was removed from the TGA and thereafter leached (onthe same day) in 431 g/l sulfuric acid at or just below 100° C. Theleach stage lasted 5 hours total. The solids and liquids were separatedby filtration and the filtrate was tested for free acid and titanium.

Table 5 summarizes the extraction of titanium from the ilmenite and theacid consumed in the experiments. TABLE 5 Extraction and AcidConsumption Results Reduction Conditions Leach Results Test Temp GasTime Weight Loss Extraction Acid Consumption STR-IR0-L1 N/a n/a N/a n/a5.25 43.11 STR-IR1-L1 450 10% H₂ in N₂ 45 1.35 6.44 41.97 STR-IR2-L1 45010% H₂ in N₂ 90 1.46 22.20 28.33 STR-IR3-L1 550 10% H₂ in N₂ 45 1.6330.84 22.62 STR-IR4-L1 550 10% H₂ in N₂ 90 1.74 35.00 18.79 STR-IR5-L1450 20% H₂ in N₂ 45 1.37 27.21 18.07 STR-IR6-L1 450 20% H₂ in N₂ 90 1.4532.19 16.94 STR-IR8-L1 550 20% H₂ in N₂ 90 2.04 36.33 20.42 STR-IR13-L1550 20% H₂ in N₂ 45 1.66 48.87 15.80

Extraction was determined as the mass of titanium present in the liquidphase after leaching, with respect to the mass available from the solidphase at the commencement of the experiment.

Sample STR-IR13-L1 is a repeat of sample STR-IR7-L1 (550° C., 20% H₂ inN₂ for 45 minutes) because the original result, i.e. sample STR-IR7-L1,was much lower than expected. The results of sample STR-IR7-L1 are notpresented here. There were two faults noted in the originalexperiment—the sample when removed from the TGA was hotter than expected(possibly causing reoxidation) and secondly the level of the water bathdropped significantly during the leach due to a poor seal between thewater bath and the lid.

Evaluation—TGA Tests.

The results of leaching ilmenite treated in accordance with theinvention in the TGA tests showed that, with the variables tested,

(a) increasing time or hydrogen concentration with the ranges testedimproved the leaching extraction of titanium from ilmenite,

(b) a combination of the two variables did not significantly furtherimprove the extraction, and

(c) increasing temperature within the range tested improved theextraction in all cases.

Hot Reduction Rig Test and Subsequent Leaching Test of Treated Material.

The impact of treatment of the first batch of the Stradbroke ilmenite inaccordance with the invention was also evaluated in a Hot Reduction Rig(HRR).

The HRR is a tube furnace that comprises a tube passing through thecentre of a Kanthal split furnace. The tube furnace has three mainsections. The upper section has a cyclone to decelerate and removeparticulates from the gas phase. A dip leg returns these solids to thebed. The sample section has a perforated plate that allows the solidsbed to be fluidised by the flow of reaction gas. The sample size isusually around 500 g mass. The lower section below the sample is filledwith stainless steel turnings. This area is designed to act as a heatexchanger to heat the reaction gas quickly to the required reactiontemperature.

The HRR differs from the TGA as the entire sample is evenly exposed to asteady stream of reaction gas. The fluidised bed avoids mass transfereffects seen in the latter stages of TGA tests. Consequently,comparisons between the TGA tests and HRR tests can be difficult, as thetime required to reach a certain reduction point in the HRR should beless than the required in the TGA.

500 g of the first batch of the unground Stradbroke ilmenite was treatedin accordance with the invention for 90 minutes under 20% H₂ in N₂ at550° C. in the HRR. At the end of the 90 minute treatment period, thetreated sample was cooled under nitrogen to 40° C., removed andthereafter leached in sulfuric acid for 5 hours on the same day in atwo-litre reactor kettle. The acid concentration was maintained at 400g/l. The kettle was maintained at a temperature of 110°0 C. The solidsloading was 400 g/l at the start of the leach.

The rate of titanium and iron dissolution exceeded any other bench testresult of the applicant to that date. The speed at which the initialreaction occurred caused the acid levels to drop below the targetacidity. The final solution containing 49 g/l titanium exceeds almostall tests thus far for concentration of titanium in solution withrespects to solids loading, time and acid concentration. Extraction oftitanium from the solids was 34% (42% when adjusted for sampling).

Comparative Performance Tests.

Experiments were carried out on the second batch of Stradbroke ilmeniteto confirm the above-described results of treatment on the first batchof Stradbroke ilmenite and to compare the results of treatment againstalternative process options.

A 500 g sample of the second batch of the Stradbroke ilmenite wastreated for 20 minutes under 20% H₂ at 550° C. in the HRR. At the end ofthe 20 minute treatment period, the treated sample was cooled undernitrogen to 40° C., removed and thereafter a 50 g sample was leached insulfuric acid for 5 hours in a two-litre reaction kettle. The kettle wasmaintained at a temperature of 110° C. The acid concentration wasmaintained at 450 g/l. The solids loading at the start of the leach was50 g/l.

A 50 g sample of the second batch of the Stradbroke ilmenite in theas-received form and a 50 g sample of the second batch of the Stradbrokeilmenite in a ground form were also leached in two-litre reactionkettles under the same conditions described in the preceding paragraph.In both cases, iron rods were added to the kettles.

Samples of the leach liquor were taken periodically during the 5 hourexperiments and were analysed to determine the extraction of titaniafrom the ilmenite into the liquor. The results are presented in FIG. 2,with the extraction expressed as g/l titanium metal in the liquor.

It is evident from FIG. 2 that the extraction of titania from the secondbatch of Stradbroke ilmenite that was treated in accordance with theinvention and subsequently leached was:

(a) comparable to that achieved with ground ilmenite; and

(b) significantly better in terms of ultimate recovery and extractionrate than the unground ilmenite.

Cruzor Ilmenite Experiments.

500 g samples of Cruzor ilmenite were fluidised with N₂ in a fluid bedreactor. The reactor was heated to a target temperature and the N₂atmosphere was replaced by reducing gas (combinations of CO, CO₂, H₂ andCH₄). After a specified time the reducing gas was replaced with N₂ andthe reactor was allowed to cool.

The product from the reactor was leached immediately in 450 g/l sulfuricacid for 48 hours at 110° C. Samples were taken at specific intervalsfor analysis to determine leaching rate and extraction.

The results of experiments on Cruzor ilmenite with reducing gas selectedto be CO are presented in FIGS. 3 and 4.

FIG. 3 is a plot of titanium extraction (%) versus leach time (hrs) forexperiments on 4 samples that were reduced under different temperatureconditions. The purpose of the Figure is to illustrate the impact ofreduction temperature on titanium extraction.

The samples shown in FIG. 3 were reduced under the following conditions.Reducing gas Temperature (° C.) pp CO = 0.45 700 pp CO = 0.45 600 pp CO= 0.45 500 Blank - N₂ only 600

FIG. 3 shows that optimum titanium extraction on leaching was obtainedwith the sample that was reduced at 600° C.

Specifically, the Figure shows that the titanium extraction on leachingthe samples reduced at 500° C. and 700° C. was significantly lower thanthat of the 600° C. reduction sample.

FIG. 4 is a plot of titanium extraction (%) versus leach time (hrs) forexperiments on 4 samples reduced under different partial pressures of COin the reducing gas. The purpose of the Figure is to illustrate theimpact of the partial pressure of CO on titanium extraction.

The samples shown in FIG. 4 were reduced under the following conditions.Reducing gas Temperature (° C.) pp CO = 0.6 600 pp CO = 0.45 600 pp CO =0.3 600 Blank - N₂ only 600

FIG. 4 shows that titanium extraction increased with partial pressure ofCO in the reducing gas with the sample reduced with a CO partialpressure of 0.6 in the reducing gas achieved the highest titaniumextraction.

The results of the above-described experiments indicate that treatmentof ilmenite in accordance with the invention is a comparable alternativeoption for accelerating the leaching rate and achieving high recoveriesof titania with low acid consumption than the current option of grindingand thereafter leaching ilmenite with scrap iron.

Many modifications may be made to the present invention described above

-   -   without departing from the spirit and scope of the invention.        While embodiments of the invention have been illustrated and        described, it is not intended that these embodiments illustrate        and describe all possible forms of the invention. Rather, the        words used in the specification are words of description rather        than limitation, and it is understood that various changes may        be made without departing from the spirit and scope of the        invention.

1. A process for producing titania from a solid, iron-containingtitaniferous material (such as ilmenite) which includes the steps of:(a) treating iron-containing titaniferous material under conditions thatreduce ferric ions to ferrous ions in the titaniferous material, theconditions including contacting the titaniferous material with areducing gas; (b) leaching treated titaniferous material and forming aleach liquor that includes an acidic solution of titanyl sulfate andiron sulfate; (c) recovering titania from the leach liquor.
 2. Theprocess defined in claim 1 wherein step (a) comprises treatingtitaniferous material under conditions that result in ferrous ions beinga predominant form of iron in the titaniferous material.
 3. The processdefined in claim 1 wherein step (a) comprises treating titaniferousmaterial under conditions that do not result in substantial formation ofrutile that is unleachable under the conditions of leaching step (b). 4.The process defined in claim 1 wherein step (a) comprises treatingtitaniferous material under conditions so that there is either nometallic iron formed in the step or a selected relatively small amountof metallic iron formed in the step.
 5. The process defined in claim 1wherein step (a) comprises treating titaniferous material by contactingtitaniferous material with the reducing gas in a fluidized bed.
 6. Theprocess defined in claim 1 wherein the reducing gas comprises anysuitable gas, such as hydrogen, carbon monoxide, and mixtures thereof.7. The process defined in claim 1 wherein the reducing gas is a mixtureof (a) hydrogen and/or carbon monoxide and/or methane and (b) anothersuitable gas such as an inert gas and/or carbon dioxide.
 8. The processdefined in claim 7 wherein the inert gas is nitrogen.
 9. The processdefined in claim 7 wherein, in a situation in which the reducing gascomprises hydrogen and the inert gas comprises nitrogen, the hydrogencomprises up to 25% by volume of the reducing gas.
 10. The processdefined in claim 1 wherein, in a situation in which the reducing gascomprises hydrogen, the temperature of the reducing gas is less than700° C. to avoid substantial formation of rutile that is unleachableunder the conditions of leaching step (b).
 11. The process defined inclaim 1 wherein, in a situation in which the reducing gas compriseshydrogen, the temperature of the reducing gas is 450-550° C.
 12. Theprocess defined in claim 7 wherein, in a situation in which the reducinggas comprises carbon monoxide and the other gas comprises carbondioxide, the carbon monoxide comprises up to 60% by volume of thereducing gas.
 13. The process defined in claim 7 wherein, in a situationin which the reducing gas comprises carbon monoxide and the inert gascomprises nitrogen, the temperature of the reducing gas is less than700° C.
 14. The process defined in claim 7 wherein, in a situation inwhich the reducing gas comprises carbon monoxide and the inert gascomprises nitrogen, the temperature of the gas is 600° C.
 15. Theprocess defined in claim 1 wherein the average contact time of thetitaniferous material and the reducing gas in step (a) is less than 120minutes.
 16. The process defined in claim 1 wherein the leaching step(b) comprises a multiple leaching step involving (i) a first step ofleaching the titaniferous material with the leach liquor and forming aprocess solution that includes an acidic solution of titanyl sulfate;(ii) separating the process solution and a residual solid phase; (iii)leaching the residual solid phase in a subsequent leach step with aleach liquor and forming a further process solution that includes anacidic solution of titanyl sulfate and iron sulfate; (iv) separating theprocess solution and a residual solid phase; and (v) supplying theseparated process solution to the first leach step and/or mixing theseparated process solution with the process solution from the firstleach step for subsequent processing in reducing step (c).
 17. Theprocess defined in claim 1 wherein the leaching step (b) includesselecting and/or controlling the leaching conditions to avoidundesirable amounts of premature hydrolysis and undesirable amounts ofpremature precipitation.
 18. The process defined in claim 1 wherein theacid concentration in the leaching step (b) is at least 350 g/l sulfuricacid throughout the leaching step when operating at a leach temperaturein the range of from 95° C. to the boiling point in order to avoidpremature hydrolysis.
 19. The process defined in claim 1 wherein theacid concentration at the end of the leaching step (b) is less than 450g/l when operating at a leach temperature in the range from 95° C. tothe boiling point in order to avoid an undesirable amount of prematureprecipitation of titanyl sulfate.
 20. The process defined in claim 1wherein the acid concentration at the start of the leaching step (b) isless than 700 g/l.
 21. The process defined in claim 1 wherein step (c)of recovering titania from the leach liquor comprises the steps of (i)separating iron sulfate from the leach liquor, (ii) separating titanylsulfate from the leach liquor either after or before step (i), and (iii)recovering titania from the titanyl sulfate.
 22. The process defined inclaim 21 wherein step (ii) of separating titanyl sulfate from the leachliquor comprises solvent extraction of titanyl sulfate from the leachliquor.
 23. The process defined in claim 21 wherein step (ii) ofseparating titanyl sulfate from the leach liquor comprises precipitatingtitanyl sulfate from the leach liquor.
 24. The process defined in claim1 wherein the leaching step (b) is in accordance with a standard sulfateprocess which includes a 2-stage step with a first stage involving solidstate sulfation of pre-treated titaniferous material from step (a) withconcentrated sulfuric acid and a second stage involving dissolving thesulfated product in water/dilute acid and forming an acidic solution oftitanyl sulfate and iron sulfate.